This invention relates to a new catalyst for the selective hydrogenation of acetylene as well as a method for making such catalyst and a method for selectively hydrogenating acetylene in admixture with ethylene.
Ethylene is a monomer that is used in preparing a number of olefin polymers. Ethylene is generally made by the pyrolysis or catalytic cracking of refinery gas, ethane, propane, butane, and the like. Ethylene, so produced, usually contains small quantities of acetylene. In polymer grade ethylene, it is generally preferred that the acetylene content be less than 5 parts per million by weight (ppmw).
One technique that has been used in the past for reducing the amount of acetylene in a stream containing ethylene is to selectively hydrogenate the acetylene using a catalyst comprising an active alumina carrier, a palladium component, and a silver component. In such a hydrogenation process, it is desirable for substantially all of the acetylene to be converted to other hydrocarbons, preferably ethylene, while only an insignificant amount of the ethylene is converted.
The selective hydrogenation of acetylene from a feed containing ethylene is promoted by the presence of carbon monoxide in the feed. Although a variety of palladium-silver catalysts have proven to be effective for selectively hydrogenating acetylene in feeds containing relatively high concentrations of carbon monoxide, many of these same catalysts are ineffective when the feed contains low concentrations of carbon monoxide (for example, less than 5 ppmw).
Because certain commercial hydrocarbon streams that contain low concentrations of carbon monoxide and high concentrations of ethylene also contain acetylene, there exists a need to develop a catalyst and process for selectively hydrogenating acetylene in such a feedstream.
An object of this invention is to provide a method, and catalyst, for the treatment of a hydrocarbon stream comprising ethylene and acetylene whereby the acetylene is selectively and substantially consumed.
A further object of the present invention is to provide such a method and catalyst whereby acetylene in admixture with ethylene is hydrogenated to form a further amount of ethylene, without the concurrent consumption of a significant portion of ethylene.
Another object of the present invention is to provide a method and catalyst suitable for selectively hydrogenating acetylene in a feedstream which contains high concentrations of ethylene and low concentrations of carbon monoxide.
In accordance with a first embodiment of the present invention a catalyst composition is provided. Such catalyst composition comprises an inorganic support material, a palladium component, a silver component, and a promoter component. The promoter component has a formula XYFn, wherein X is an alkaline metal, Y is an element selected from the group consisting of antimony, phosphorus, boron, aluminum, gallium, indium, thallium, and arsenic, and n is an integer which makes YFn a monovalent anion.
In a second embodiment of the present invention a process is provided. Such process comprises contacting, under acetylene hydrogenation conditions, a feed comprising ethylene and acetylene with the catalyst described in the first embodiment of the present invention.
In a third embodiment of the present invention a process for making a catalyst composition is provided. Such process comprises incorporating a palladium component, a silver component, and a promoter component, described in the first embodiment of the present invention, into an inorganic support.